/** Initialize the current thread as a looper. * This gives you a chance to create handlers that then reference * this looper, before actually starting the loop. Be sure to call * {@link #loop()} after calling this method, and end it by calling * {@link #quit()}. */ publicstaticvoidprepare(){ prepare(true); }
privatestaticvoidprepare(boolean quitAllowed){ if (sThreadLocal.get() != null) { thrownew RuntimeException("Only one Looper may be created per thread"); } sThreadLocal.set(new Looper(quitAllowed)); }
privateLooper(boolean quitAllowed){ mQueue = new MessageQueue(quitAllowed); mThread = Thread.currentThread(); }
/** * Use the {@link Looper} for the current thread with the specified callback interface * and set whether the handler should be asynchronous. * * Handlers are synchronous by default unless this constructor is used to make * one that is strictly asynchronous. * * Asynchronous messages represent interrupts or events that do not require global ordering * with respect to synchronous messages. Asynchronous messages are not subject to * the synchronization barriers introduced by {@link MessageQueue#enqueueSyncBarrier(long)}. * * @param callback The callback interface in which to handle messages, or null. * @param async If true, the handler calls {@link Message#setAsynchronous(boolean)} for * each {@link Message} that is sent to it or {@link Runnable} that is posted to it. * * @hide */ publicHandler(Callback callback, boolean async){ if (FIND_POTENTIAL_LEAKS) { final Class<? extends Handler> klass = getClass(); if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) && (klass.getModifiers() & Modifier.STATIC) == 0) { Log.w(TAG, "The following Handler class should be static or leaks might occur: " + klass.getCanonicalName()); } }
mLooper = Looper.myLooper(); if (mLooper == null) { thrownew RuntimeException( "Can't create handler inside thread that has not called Looper.prepare()"); } mQueue = mLooper.mQueue; mCallback = callback; mAsynchronous = async; }
/** * Use the provided {@link Looper} instead of the default one and take a callback * interface in which to handle messages. Also set whether the handler * should be asynchronous. * * Handlers are synchronous by default unless this constructor is used to make * one that is strictly asynchronous. * * Asynchronous messages represent interrupts or events that do not require global ordering * with respect to synchronous messages. Asynchronous messages are not subject to * the synchronization barriers introduced by {@link MessageQueue#enqueueSyncBarrier(long)}. * * @param looper The looper, must not be null. * @param callback The callback interface in which to handle messages, or null. * @param async If true, the handler calls {@link Message#setAsynchronous(boolean)} for * each {@link Message} that is sent to it or {@link Runnable} that is posted to it. * * @hide */ publicHandler(Looper looper, Callback callback, boolean async){ mLooper = looper; mQueue = looper.mQueue; mCallback = callback; mAsynchronous = async; }
/** * Run the message queue in this thread. Be sure to call * {@link #quit()} to end the loop. */ publicstaticvoidloop(){ final Looper me = myLooper(); if (me == null) { thrownew RuntimeException("No Looper; Looper.prepare() wasn't called on this thread."); } final MessageQueue queue = me.mQueue;
// Make sure the identity of this thread is that of the local process, // and keep track of what that identity token actually is. Binder.clearCallingIdentity(); finallong ident = Binder.clearCallingIdentity();
for (;;) { Message msg = queue.next(); // might block if (msg == null) { // No message indicates that the message queue is quitting. return; }
// This must be in a local variable, in case a UI event sets the logger Printer logging = me.mLogging; if (logging != null) { logging.println(">>>>> Dispatching to " + msg.target + " " + msg.callback + ": " + msg.what); }
msg.target.dispatchMessage(msg);
if (logging != null) { logging.println("<<<<< Finished to " + msg.target + " " + msg.callback); }
// Make sure that during the course of dispatching the // identity of the thread wasn't corrupted. finallong newIdent = Binder.clearCallingIdentity(); if (ident != newIdent) { Log.wtf(TAG, "Thread identity changed from 0x" + Long.toHexString(ident) + " to 0x" + Long.toHexString(newIdent) + " while dispatching to " + msg.target.getClass().getName() + " " + msg.callback + " what=" + msg.what); }